1. Field of the Invention
The present invention relates generally to ultrasonic dental scalers and more particularly to the vibrating components of the scaler handpieces.
2. Description of the Prior Art
Ultrasonic dental scalers usually comprise a dental handpiece having an ultrasonic transducer positioned with an energizing coil located within a sleeve. The transducer conventionally comprises a stack of laminar plates of magnetostrictive material that is excited by the coil to longitudinally expand and contract at a frequency of approximately 20,000 cycles per second.
The transducer stack is connected at one end to an acoustical impedance transformer which in turn is connected to a dental work tool, all of which comprises the electromechanical vibrator. The transformer provides an acoustical transmission line between the transducer and the work tool. The vibrator is typically mounted in the sleeve by means of an o-ring located at a node of longitudinal vibration of the transformer when compression waves of the operating frequency are generated by the transducer. For maximum amplitude of vibration of the tool end, and for maximum transmission of working energy, the overall length of the transducer, transformer and work tool is so correlated to the frequency of the electrical oscillations delivered to the transducer, that a loop of motion of the generated compressional waves will occur at or near the working end of the tool. In other words, the overall length of the vibrator is approximately equal to an integral number of one-half wavelengths of sound waves in the particular materials comprising these components at the working frequency. The length of the transducer is also an integral number of one-half wavelengths -- typically one-owing to the desire to provide the least massive system possible. It may be appreciated that size and mass are important considerations in a field in which delicate work requires instruments having an ease of handling.
In conventional dental scalers, the entire length of the vibrator is approximately 6 to 7 inches. Although it is desirable to shorten this length to make a smaller, more compact handpiece, the frequency of the system would increase to over 40,000 cycles per pound. This frequency range is considered unacceptable for dental practice.